I don't know the answer but if I cared to guess, it might be because the talent pool for orchestra performers had significantly more gender parity than the talent pool competing for elite engineering jobs at Google.

Edit: Google says that their diversity platform is non-discriminatory because they're not changing their standards, but rather looking harder for qualified diversity candidates (paraphrasing). This makes the gargantuan and probably unwarranted assumption that there are a lot of these candidates not applying and that 'looking harder' will find them.